Control brightness and contrast of a monitor exposing DDC over an FTDI F232H.

ddc-ftdi.py

#!/usr/bin/python3

"""Control brightness and contrast of a monitor exposing DDC over an FTDI F232H.

Usage:
    ddc-ftdi.py [<brightness> <contrast>]

Arguments:
    <brightness>   Brightness value to set (0..100)
    <contrast>     Contrast value to set (0..100)
"""

from pyftdi.i2c import I2cController
import pyftdi.misc
import time
import sys

def checksum(data, addr):
	sum = addr
	for c in data:
		sum = sum ^ c
	return sum

def ftdi_init():
	i2c = I2cController()
	i2c.configure('ftdi://ftdi:232h/1', frequency=100000.0)
	print("Opened i2c connection at {}Hz".format(i2c.frequency))
	return i2c.get_port(0x37)

def ddc_write(slave, message, sleep=0.04):
	x = message + bytes({checksum(message, 0x6E)})
	print("Writing: {}".format(pyftdi.misc.hexline(x)))
	slave.write(x)
	time.sleep(sleep)

def ddc_read(slave):
	data = slave.read(2)
	if data[0] != 0x6E:
		raise IOError("Unexpected reply from address {}".format(data[0]))
	data = data + slave.read((data[1] & 0x7F) + 1)
	x = checksum(data, 0x50)
	print("Read: {}".format(pyftdi.misc.hexline(data)))
	if x != 0:
		print("BAD checksum: got {})".format(x))
	return data

def ddc_query(slave, message, sleep=0.04):
	ddc_write(slave, message, sleep)
	return ddc_read(slave)

# http://www.boichat.ch/nicolas/ddcci/specs.html
controls = {
    'brightness': 0x10,
    'contrast': 0x12
}

def get_value(slave, control):
	message = b'\x51\x82\x01' + bytes({control})
	data = ddc_query(slave, message)
	print("Maximum: {}, Current: {}".format(data[7], data[9]))

def set_value(slave, control, value):
	message = b'\x51\x84\x03' + bytes({control}) + b'\x00' + bytes({value})
	data = ddc_write(slave, message)

def main():
	if len(sys.argv) != 3:
		brightness = 75
		contrast = 50
	else:
		brightness = int(sys.argv[1])
		contrast = int(sys.argv[2])

	slave = ftdi_init()

	get_value(slave, controls['brightness'])
	set_value(slave, controls['brightness'], brightness)

	get_value(slave, controls['contrast'])
	set_value(slave, controls['contrast'], contrast)

if __name__=="__main__":
	main()